The present invention relates to contacts for trenches that may be used in semiconductor devices to isolate portions of the device and to methods of contacting the trenches, and more particularly to contact regions and methods for electrically contacting the conductive material in trenches that are too narrow for conventional electrical contacts.
A semiconductor device may include one or more trenches for isolating portions of the device. As may be seen in FIGS. 1 and 2, a semiconductor device 10 (e.g., a silicon substrate wafer) may include a portion 12 that is to be isolated from other portions 14 by a trench 16 that is filled with a conductive material 18, such as polysilicon. An insulator 20 is typically provided to separate the portions from the conductive material 18. The trench 16 may take any suitable shape, although such trenches typically have near vertical sides, such as illustrated in the figures.
There are various reasons for using trenches filled with a conductive material to separate portions of the device. For example, each of the portions 12 and 14 may be dielectrically isolated and biased at its optimum voltage, while the conductive material 18 in the trench may be biased at a voltage that reduces high-low junction and corner breakdown limitations in the adjacent portions. Other uses for such trenches are known and need not be discussed herein. See, for example, U.S. Pat. Nos. 5,057,895 and 5,196,373 for additional discussion of trenches.
The conductive material 18 in the trench is provided with a contact region so that the appropriate electrical connections can be made. Some semiconductor devices may include an insulative layer 22 overlying the isolated portions 12 and 14 and trenches 16, and appropriate biasing voltage may be provided to the portions and the conductive material through separate contact apertures in the insulative layer 22 (e.g., aperture 24 to the portion 12, and aperture 26 to the conductive material 18). An electrically conductive terminal 28 may be provided that extends through the aperture 26 into contact with the conductive material 18 in the trench.
The selection of an appropriate size and shape for the contact region for the conductive material in the trenches presents problems with conflicting solutions. As is apparent, trenches take up real estate on the surface of the semiconductor device and it is desirable to reduce the size of the trenches to save the real estate for operational components. This may be achieved by reducing their width W.sub.1 (their depth and length being difficult to change and determined by the size and arrangement of the isolated portions in the device). The width is determined, at least in part, by the method of forming the trench (such methods being known and need not be discussed herein) and the presence of a contact diffusion area 30 that may provide a width limit for narrow trenches.
Narrow trenches that are uniform in width, or nearly so, are also desirable because the amount of conductive material needed to fill them is less than needed to fill trenches that are not uniformly narrow. Trenches are typically filled by applying a layer of conductive material on top of the semiconductor device, and thereafter removing the conductive material remaining on top of the device, leaving it in the trenches. The width of the widest trench determines the thickness of the conductive material that is to be applied over the entire surface of the semiconductor device. That is, even if a trench includes only a small section that is wider than the rest of the trench, the material used to make the trench must be applied to the thickness needed for the widest section.
However, trenches with narrow widths are very difficult to contact electrically. (Were it not for the desirability of having nearly uniformly narrow trenches, an obvious solution would be to make a portion of the trench wider for an electrical contact region.) The electrical contact to the conductive material in the trench should contact only that material and not adjacent portions of the semiconductor device or the peripheral insulator, and thus it is necessary to make the contact region narrower than the trench. It is also necessary to take into account the manufacturing alignment tolerance encountered during fabrication of the devices (one tolerance on each side of the contact; hereinafter twice the manufacturing alignment tolerance is referred to as the alignment tolerance). Thus, trenches are desirably uniformly narrow to reduce real estate and the cost of manufacturing. On the other hand, the trenches must be able to be electrically contacted. Heretofore, a satisfactory solution to these conflicting goals has not been achieved.
Accordingly, it is an object of the present invention to provide a novel trench contact and method of contacting and making the trenches that obviate the problems of the prior art.
It is another object of the present invention to provide a novel trench contact and method of contacting and making the trenches in which an electrical contact region of sufficient size is provided without increasing the width of the trenches.
It is yet another object of the present invention to provide a novel trench contact and method of contacting and making the trenches in which a narrow trench is divided into two spaced apart trench sections, each section having the same narrow width as the first trench, the combined width of the two trench sections and the space therebetween being sufficient for a contact region.
It is yet a further object of the present invention to provide a novel trench contact and method of contacting and making the trenches in which a trench of predetermined width is provided with a section wider than the predetermined width, the section including at least one island surrounded on its sides by the trench of predetermined width.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.